1 files changed, 29 insertions, 0 deletions
diff --git a/debuggerd/utility.cpp b/debuggerd/utility.cpp
index 9f340a8..236d667 100644
--- a/debuggerd/utility.cpp
+++ b/debuggerd/utility.cpp
@@ -20,6 +20,7 @@
 
 #include <errno.h>
 #include <signal.h>
+#include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 #include <sys/ptrace.h>
@@ -207,3 +208,31 @@ void dump_memory(log_t* log, Backtrace* backtrace, uintptr_t addr, const char* f
     _LOG(log, logtype::MEMORY, "%s  %s\n", logline.c_str(), ascii.c_str());
   }
 }
+
+bool pid_contains_tid(pid_t pid, pid_t tid) {
+  char task_path[PATH_MAX];
+  if (snprintf(task_path, PATH_MAX, "/proc/%d/task/%d", pid, tid) >= PATH_MAX) {
+    ALOGE("debuggerd: task path overflow (pid = %d, tid = %d)\n", pid, tid);
+    exit(1);
+  }
+
+  return access(task_path, F_OK) == 0;
+}
+
+// Attach to a thread, and verify that it's still a member of the given process
+bool ptrace_attach_thread(pid_t pid, pid_t tid) {
+  if (ptrace(PTRACE_ATTACH, tid, 0, 0) != 0) {
+    return false;
+  }
+
+  // Make sure that the task we attached to is actually part of the pid we're dumping.
+  if (!pid_contains_tid(pid, tid)) {
+    if (ptrace(PTRACE_DETACH, tid, 0, 0) != 0) {
+      ALOGE("debuggerd: failed to detach from thread '%d'", tid);
+      exit(1);
+    }
+    return false;
+  }
+
+  return true;
+}